U.S. patent number 5,268,545 [Application Number 07/993,192] was granted by the patent office on 1993-12-07 for low profile tactile keyswitch.
This patent grant is currently assigned to Lexmark International, Inc.. Invention is credited to David A. Bruner.
United States Patent |
5,268,545 |
Bruner |
December 7, 1993 |
Low profile tactile keyswitch
Abstract
A low profile tactile keyswitch including a horizontally
positioned elastic column spring which buckles under an axial load
to provide a tactile feel for the keyswitch. The ends of the spring
are maintained between two spring holders which are urged together
as the keybutton is depressed. Stabilizing arms pivotally attached
to the keybutton are used to stabilize the keybutton and also to
carry extensions which engage the spring holders to move them
together as the keybutton is depressed. The keyswitch is operable
to be placed in an inactive configuration in which the keybutton is
lowered without placing the spring under added compression.
Inventors: |
Bruner; David A. (Versailles,
KY) |
Assignee: |
Lexmark International, Inc.
(Greenwich, CT)
|
Family
ID: |
25539210 |
Appl.
No.: |
07/993,192 |
Filed: |
December 18, 1992 |
Current U.S.
Class: |
200/345; 200/329;
200/344; 200/517; 200/521; 400/490; 400/491.2 |
Current CPC
Class: |
H01H
13/705 (20130101); H01H 3/125 (20130101); H01H
2013/525 (20130101); H01H 2235/012 (20130101); H01H
2221/068 (20130101); H01H 2227/036 (20130101); H01H
2221/058 (20130101) |
Current International
Class: |
H01H
13/70 (20060101); H01H 13/705 (20060101); H01H
3/02 (20060101); H01H 3/12 (20060101); H01H
013/70 () |
Field of
Search: |
;200/341,342,344,345,517,329,520,521,327,408,409,453,454,457,43.11,318.1,318.2
;400/496,490,491.1,491,491.2,491.3,495,495.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1424065 |
|
Sep 1988 |
|
SU |
|
2057767 |
|
Apr 1981 |
|
GB |
|
Other References
IBM Technical Disclosure Bulletin, vol. 17, No. 11, Apr. 1975, pp.
3377-3378, entitled "Low-Force Displacement Capacitor Actuator For
Calico Keyboards" by R. H. Harris. .
IBM Technical Disclosure Bulletin, vol. 31, No. 7, Dec. 1988, pp.
304-306, entitled "Keybutton Stabilizer" by D. A. Bruner..
|
Primary Examiner: Recla; Henry J.
Assistant Examiner: Barrett Glen T.
Attorney, Agent or Firm: McArdle, Jr.; John J.
Claims
I claim:
1. A key mechanism comprising:
a key top;
an elastic column element, generally beneath the key top, which
buckles under an axial load;
means, including a force-receiving surface, for holding the elastic
column element under precompression in a first orientation and
responsive to an applied force, on the force-receiving surface, to
further compress the elastic column into a buckled condition;
and stabilizing means for supporting the key top including two
pivoted stabilizing arms pivotally attached to the key top and to
one another, movement of the key top in a direction generally
perpendicular to the orientation of the elastic column element
resulting in movement of portions of the pivoted arms, the
stabilizing means further including at least one element coupled to
a moving portion of a stabilizing arm which engages the
force-receiving surface of the means for holding the elastic column
element to apply a force to the means for holding the elastic
column element to further compress the elastic column element into
a buckled condition.
2. The key mechanism of claim 1 in which the elastic column element
is a buckling compression spring and in which the means for holding
the elastic column under precompression comprises a first spring
holder receiving a first end of the compression spring and a second
spring holder receiving a second end of the compression spring, at
least one of the spring holders being movable toward the other
spring holder in response to an applied force by said one element
to further compress the spring into a buckled condition.
3. The key mechanism of claim 2 which includes a base and in which
at least one of the spring holders is rotatably mounted on the
base, permitting said spring holder to rotate in a direction toward
the other spring holder.
4. A key mechanism comprising:
a key top;
an elastic column element;
means, including a force-receiving surface, for holding the elastic
column element, generally beneath the key top, under precompression
in a first orientation and responsive to an applied force on the
force-receiving surface to further compress the elastic column
element into a buckled condition;
a base lying in a plane generally beneath the elastic column
element;
a first and a second stabilizing arm, the first stabilizing arm
being pivotally attached at a first end to the key top near an edge
thereof and the second arm being pivotally attached at a first end
to the key top near another edge thereof, each arm being pivotally
attached to the other at a second end;
and means for pivotally supporting each of the arms intermediate
their ends in positions above the base, at least one said arm
including an element contacting the force-receiving surface of the
means for holding the elastic column under precompression so that
downward movement of the key top results in application of a force
to the force-receiving surface of the means for holding the elastic
column element under precompression to further compress the elastic
column element into a buckled condition.
5. The key mechanism of claim 4 in which the elastic column element
is a buckling compression spring and in which the means for holding
the spring under precompression includes a first spring holder and
a second spring holder mounted on the base generally between the
base and the key top.
6. A key mechanism comprising:
a key top;
a buckling compression spring;
means, including a force-receiving surface, for holding the spring
under precompression generally horizontally in a first condition
and responsive to an applied force on the force-receiving surface
to further compress the spring into a buckled condition;
and means coupled to the key top for converting movement of the key
top, in a generally vertical direction into a force applied to the
force-receiving surface of the means for holding the spring,
whereby the spring is further compressed into a buckled
condition.
7. A key mechanism comprising:
a key top;
tactile feedback means, having a force-receiving surface,
responsive to an applied force on the force-receiving surface for
providing a variable resistance to said force;
stabilizing means for supporting the key top and including means
for applying a force to the force-receiving surface of the tactile
feedback means when the key top is depressed;
and means for changing the relative orientation between the
stabilizing means and the tactile feedback means to an inactive
relative orientation in which depression of the key top does not
result in the application of said force to the force-receiving
surface of the tactile feedback means.
8. The key mechanism of claim 7 in which the tactile feedback means
is an elastic column element which buckles under an axial load and
means for holding the elastic column element under precompression
in a first orientation, said means for holding the elastic column
having said force-receiving surface and being responsive to said
applied force on said force-receiving surface to further compress
the elastic column into a buckled condition, and in which the
stabilizing means includes at least one element which is positioned
to apply said force to said force-receiving surface of the means
for holding the elastic column element when the key top is
depressed.
9. The key mechanism of claim 8 in which the elastic column element
is a buckling compression spring and in which the means for holding
the elastic column element under precompression comprises a first
spring holder receiving a first end of the compression spring and a
second spring holder receiving a second end of the compression
spring, and in which the means for changing the relative
orientation between the stabilizing means and the tactile feedback
means comprises means for translating the first and second spring
holders relative to said one element so that, in an inactive
configuration of the key mechanism, said one element does not
engage either of the spring holders.
Description
BACKGROUND OF THE INVENTION
One generally accepted type of keyswitch for typewriters and
computer keyboards is referred to as a tactile keyswitch. Tactile
keyswitches provide a crisp tactile force and acoustic response
when depressed by an operator. Such tactile keyswitches can be
constructed in various ways.
One of the most widely utilized tactile keyswitch mechanisms is the
"buckling spring" mechanism. As described in, for example, U.S.
Pat. No. 4,118,611, a buckling spring keyswitch provides a
non-teasible, snap-action, tactile feedback key mechanism featuring
the use of a catastrophically buckling compression column
spring.
This keyswitch mechanism is one of the most preferred for use in
data entry keyboards. Because of the design of this mechanism in
its current implementation, however, it is not well suited for very
thin or low profile keyboard applications such as notebook computer
products. Currently, buckling spring keyboards have a minimum
thickness of about one inch.
Low profile notebook computer products typically specify keyboard
thicknesses of less than one half inch. The thinnest "full travel"
notebook keyboard product which is typical of what is in use in the
keyboard industry has a thickness of 11 millimeters (0.433 inches).
Keyboards are known which are of thicknesses as small as 8.4
millimeters (0.33 inches). Virtually all of these low profile
keyboards utilize a pseudo-tactile rubber dome keyswitch
mechanism.
The components of keyboard thickness are primarily keybutton
height, keybutton travel and bearing length. The keybutton height
for low profile keyboards is typically within a narrow range from 4
millimeters to 5 millimeters (0.16 inches to 0.2 inches). This is
considered to be the minimum thickness for a keybutton in order for
it to have good aesthetic characteristics. The keystroke, or
travel, of keys in low profile keyboards is usually in the range of
2.0 millimeters to 3.3 millimeters (0.08 inches to 0.13 inches).
The travel of keys in desktop keyboards where there is no thickness
limitation, designated "full travel", has historically been 3.5
millimeters to 4.0 millimeters (0.14 inches to 0.16 inches).
However, it is not uncommon to claim full travel for keyboards
having a keystroke as small as 3.3 millimeters (0.13 inches).
Keyboards which have little or no travel, less than 1 millimeter
(0.04 inches), are usually considered insufficient for touch
typing.
Referring to FIG. 1, an exemplary prior art low profile rubber dome
keyswitch 11 for a low profile keyboard includes a keybutton 12
having a stem 13 received in a housing, or bearing 14. The keyboard
thickness 16 is 11 millimeters, the keybutton height 17 is 4
millimeters, and the travel 18 is 2.5 millimeters.
For a given keybutton height and travel, the remaining limiting
factor in reducing keyboard height is the bearing length of the
keybutton bearing. In the present example, the bearing length 19 is
2.65 millimeters. The function of the bearing is to keep the
keybutton top surface perpendicular to the direction of travel of
the key as the keybutton is depressed. This function is referred to
as stabilization. If the bearing is too short stabilization is
degraded, and noticeable binding forces appear when the button is
actuated at the periphery of the strike surface on the key top.
This bearing height limitation can be overcome through the use of
more complex stabilization designs. One such design is a
telescoping sleeve bearing which allows the bearing to collapse as
the keybutton is depressed. This technique has been used to produce
9 millimeter (0.354 inches) thickness keyboards; but this technique
seems to provide little hope for much additional height reduction.
Another approach which is known to enable thinner constructions, at
the expense of added complexity, is to employ stabilizing schemes
already in use for long keybuttons, such as the space bar. These
designs exist in many forms, but in general use pivoting arms or
links to transfer the deflection motion of one end of the keybutton
to the other end, thereby maintaining the proper orientation of the
top surface of the keybutton.
It is an objective of the present invention to provide a tactile
keyswitch for keyboards of the foregoing type which will provide a
lower profile keyboard assembly than present pseudo-tactile rubber
dome keyswitches.
In order to accomplish this, a keyswitch is provided which employs
a horizontally positioned elastic column which buckles under an
axial load to provide the tactile nature of the keyswitch
mechanism. In a particular embodiment of the invention, a buckling
spring serves as the elastic column and is placed horizontally
rather than vertically in the tactile keyswitch mechanism.
In one form of the invention, the ends of the spring are
constrained between two caps which are urged together as the
keybutton is depressed. Stabilizing arms pivotally attached to the
keybutton are used instead of a bearing to provide stabilization,
and these stabilizing arms also carry extensions which engage the
caps to move them together as the keybutton is depressed.
An exemplary form of the invention will now be described, in
conjunction with the accompanying figures, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic side view of a prior art rubber dome key
structure;
FIG. 2 is an exploded view of a key mechanism in accordance with
the present invention;
FIG. 3 is a top view, with portions removed, of the key mechanism
of FIG. 2 with the key in its active configuration and the
keybutton underpressed;
FIG. 4 is a front elevational view, with portions removed, of the
key mechanism of FIG. 3;
FIG. 5 is a side elevational view of the key mechanism of FIG.
3;
FIG. 6 is a top view, with portions removed, of the key mechanism
of FIG. 2 in an active configuration with the keybutton
depressed;
FIG. 7 is a top view, with portions removed, of the key mechanism
of FIG. 2 in its inactive configuration;
FIG. 8 is a front elevational view, with portions removed, of the
key mechanism of FIG. 7; and
FIG. 9 is a side elevational view of the key mechanism of FIG.
7.
DETAILED DESCRIPTION
With reference to the figures, and particularly FIGS. 2-5, in an
exemplary embodiment of the invention, a helical compression column
spring 21 is mounted horizontally in a key assembly 22. The ends of
the spring 21 are held in spring holders 23, 24, which are acted
upon by key top stabilization elements that include stabilization
arms 28, 29. Extension pins 26, 27 from the stabilization arms 28,
29 serve to force the spring holders 23, 24 to swing toward one
another as the keybutton, or key top, 31 is depressed. Forcing the
spring holders together causes the spring to be compressed, and
eventually to buckle.
The stabilization elements, in addition to stabilizing the
keybutton as shall be described, function to convert the vertical
motion of the keybutton to a horizontal motion which is needed to
compress the horizontally-oriented spring 21. In this way, the
force change from the deflected spring as it buckles is transferred
back to the keybutton, providing a tactile keyswitch.
The geometry of the spring 21 and spring holders 23, 24 is such
that the buckling of the spring is in a plane generally parallel to
the plane of the base of the keyboard. The advantage of buckling in
this plane is that the total thickness occupied by the spring is
only its own thickness, regardless of whether the spring is in its
buckled or unbuckled condition.
The spring holders 23 and 24 are substantially identical, being
mirror images of one another. Considering one of the spring
holders, the spring holder 23 for example, in more detail, the
spring holder includes a spring-retaining portion 32 at the end of
an arm portion 33 which terminates in a pivot post portion 34. The
spring-retaining portion 32 includes a top wall 40 as well as a
rear wall, which cooperate to form a "pocket" to hold the spring
21. An elongated stud 45 formed inside the side wall of the portion
32 limits movement of the end of the spring in the pocket. The
pivot post 34 serves as the pivot point for rotation of the spring
holder 23 in a horizontal plane as the spring-retaining portion 32
and a corresponding spring-retaining portion 30 (in the other
spring holder 24) move toward one another when the key is
depressed. Extending outwardly from the end of the spring-retaining
portion 32 is a force-receiving tab 36 to which a force is applied
by the pin 26 when the key is depressed. The pin 27 exerts a
similar force on a tab 35 on the spring holder 24 when the key is
depressed.
The base of the keyboard includes, for present purposes, three
layers: a bottom layer 38, a top layer 39 and a middle layer 37,
which is movable relative to the other two layers. The spring
holders 23, 24 are mounted for rotation in the moving layer 37
above the bottom layer 38 of the keyboard. The bottom layer of the
keyboard contains, for each key assembly 22, a membrane switch (not
shown), which is actuated in a manner to be described subsequently
when the key is depressed. The layers 39 and 37 are apertured in
the vicinity of the keybutton 31, while the bottom layer is
substantially continuous, as best seen in FIG. 2.
The top layer 39 of the keyboard base is fixed above, and spaced
apart from, the moving layer 37 to support stabilization elements
41 and 42, which include the stabilization arms 28, 29,
respectively. The top layer 39 is suitably secured, for example,
about the periphery of the keyboard, and also through slotted
openings in the moving layer 37, to the bottom layer 38. For each
key, the top layer includes two pairs of bearing elements 43, 44
and 46, 47 for the stabilizer elements 41, 42, respectively. The
bearing elements are integrally formed with the top layer 39.
The stabilizer 41 includes the stabilization arm 28 and a
stabilization arm 48, each of which is formed integrally with a
cross member 49. There is an outwardly extending pin portion 51
(FIG. 5) in line with the cross member 49 on the stabilization arm
28, and there is an outwardly extending pin portion 52 similarly
aligned on the stabilization arm 48. The pin portion 51 is received
in the bearing 43 and the pin portion 52 is received in the bearing
44.
One end of the stabilization arm 28 includes an outwardly extending
pin portion 53 which is retained for rotation and translation in a
socket portion 71 located on the inside of the key cap 31. The
stabilization arm 48 has at an end an outwardly extending pin
portion 54 axially aligned with the pin portion 53 and received in
another socket 72 in the key cap 31. At the other end of the
stabilization arm 28, a pin portion 56 (FIG. 3) is received in a
bearing portion 57 on the stabilization arm 29. Similarly, at the
end of the stabilization arm 48 opposite the pin portion 54, is a
pin portion 58 which is received in a bearing portion 59 on a
stabilization arm 61, which is part of the stabilizer 42.
As in the case of the stabilizer 41, the stabilizer 42 includes a
cross member 62. There is an outwardly extending pin portion 63 in
line with the cross member 62 on the stabilization arm 29, and
there is an outwardly extending pin portion 64 similarly aligned on
the stabilization arm 61. The pin portion 63 is received in the
bearing 46 on the top base layer 39, and the pin portion 64 is
received in the bearing 47 on the top base layer 39. Each of the
pin portions 51, 52, 63 and 64 is received for rotation and
translation in an elongated oval channel in a different one of the
bearings 43, 44, 46 and 47.
The stabilization arm 29 includes, at its end opposite the end
carrying the bearing 57, an outwardly extending pin portion 65
which is retained for rotation and translation in a socket 73
inside the key cap 31. The stabilization arm 61 includes, at its
end opposite the end forming the bearing 59, an outwardly extending
pin portion 66 axially aligned with the pin portion 65 received on
a socket 74 (FIG. 4) inside the key cap 31.
Each stabilizer 41 and 42 is integrally formed as a single plastic
molded part. The two stabilizers are attached for pivoting relative
to one another at the pin and socket connections 56, 57 and 58, 59.
Also, the key cap 31 is a single molded part formed to include the
sockets 71-74 located generally at lateral edges thereof and a
downwardly extending post 70. The sockets 71-74 each have an
elongated oval interior shape to permit rotation and translation of
the pin portions therein. The post 70 is aligned with a membrane
switch (not shown) in the bottom layer 38 of the base of the
keyboard when the key cap is depressed.
With continued reference to FIGS. 3-5, in the assembled key
mechanism 22 the key cap 31 is supported and stabilized by the
stabilizers 41 and 42, which are in turn supported on the bearings
such as 43 and the spring holders such as 23. The key cap 31 is
supported by the retention of the pins such as 53 in the sockets
such as 71 and the stabilizer assembly (made up of the stabilizers
41 and 42) is supported by the retention of the pins such as 51 in
the bearings such as 43. The key cap 31 is held in the upright
position, as best shown in FIGS. 4 and 5, and the stabilizer
assembly kept from collapsing, due to the resting of the extension
pins 26 and 27 upon the tabs 35 and 36 on the spring holders 23 and
24. The tabs and spring holders are held apart by the partially
compressed helical compression spring 21.
When the key cap 31 is depressed, the stabilizer joints 56, 57 and
58, 59 move upwardly and the extension pins 26, 27 swing inwardly
forcing the spring holders 23 and 24 to rotate toward one another,
compressing the spring 21. As the key is depressed, and the
compression in spring 21 increases, the spring buckles (FIG. 6)
providing tactile feedback to a person depressing the key. When the
key is depressed, the post 70 passes through the openings in the
layers 37 and 39 of the keyboard base, striking the bottom layer 38
and closing a membrane switch (not shown) in the bottom layer 38.
When the key is released, the force of the spring 21 spreads the
spring holders 23 and 24 apart, swinging the extension pins 26, 27
outwardly, returning the key to the orientation shown in FIGS. 4
and 5.
Each spring holder 23, 24 lies within openings in the upper two
layers 39 and 37 of the keyboard base. The spring holder 23, for
example, rests upon the top surface 82 of the bottom layer 38 of
the base of the keyboard. The pivot post portion 34 of the spring
holder 23 has a lower portion which extends through an aperture 84
in the middle layer 37 of the keyboard base in a manner to secure
the spring holder for rotation about the pin portion 34. Outward
rotational movement of each spring holder such as 23 is limited by
a stop surface such as 83 formed along a portion of the inner wall
of the opening in the top layer 39.
With additional reference to FIGS. 7-9, the middle layer 37 may be
moved (downwardly as shown in FIG. 7) to permit the key mechanism
22 to be placed in an inactive, collapsed, low profile condition.
This permits the keyboard to assume a low profile for storage
without maintaining the springs 21 in a stressed, buckled
condition.
Movement of the middle layer 37 relative to the fixed layers 38 and
39 (downwardly as viewed in FIG. 7 and to the left as viewed in
FIG. 9) slides the tabs such as 36 from beneath the extension pins
such as 26, allowing the stabilizer assembly 41, 42 to collapse.
The extension pins such as 26 swing inwardly into openings such as
85 in a portion 87 of the moving layer 37 when the key mechanism 22
is placed in its inactive configuration.
When the moving layer 37 is moved in the other direction to return
the key mechanism to an active configuration, each extension pin
such as 26 rides along a cam surface such as 86 on one side of the
opening 85 so that the extension pin is lifted back up onto the tab
36 to assume the active configuration.
In the illustrated form of the invention, the base layers 37, 38
and 39 have been shown with exaggerated spacings between the layers
for purposes of illustration. The bottom layer 38, while shown as a
single element for the purpose of illustrating the inventive key
mechanism, would typically be an aluminum sheet with suitable
overlays to provide membrane (or other) switches and conductive
paths for the switches. It is presently contemplated that the
spring 21 and the moving layer 37 would be metal and the remainder
of the parts plastic, but changes and modifications to the parts
and the materials used to form the parts may be made without
departing from the spirit of the invention. For example, some parts
making up the illustrated key mechanism which are shown as single
components may be formed from two or more elements if desired to
facilitate assembly of the key mechanism. Also, other switch
actuation techniques beyond having the post 70 strike a membrane
switch could be employed.
* * * * *